1. Field of the Invention
The present invention relates to a program circuit and, more particularly, to a program circuit which can prevent a lowering of reliability occurring during the process of verifying the programmed data.
2. Description of the Prior Arts
Generally, a flash memory device has functions of electrical program and erasure. The flash memory device also performs a verification operation so as to confirm whether the memory cell has been programmed or erased or not after completion of the programming or the erasure operation. At this time, if there are memory cells in which a programming or erasure operation has not completed, re-programming or re-erasure operation is performed again.
In a conventional flash memory device, however, a program bias voltage is applied to a memory cell which is already programmed during a re-programming operation, thus the already programmed memory cell is damaged. This is because the program bias voltage of high voltage is applied to the memory cell, therefore, charge is trapped at the tunnel oxide film of the memory. As a result, reliability of the memory cell is degraded.